Description: A non-invasive ophthalmic instrument that measures the inability of cataractous eyes to produce clear images is greatly needed. A prototype instrument was developed in Phase I to measure the width of the Line Spread Function (LSF) formed on the retina. In clinical studies, the LSF-width was found to be correlated with several indicators of cataract development, namely 1) increased glare sensitivity, 2) loss of contrast sensitivity, 3) loss of visual acuity, and 4) increased lens opacification observed with the slit lamp. In Phase II, we will refine the instrument by developing a more sensitive detection method that will allow the Modulation Transfer Function (MTF) to be accurately determined. Clinical studies will be conducted, 1) to investigate if a patient's contrast sensitivity (CS) function (determined by chart testing) can be predicted from the optical MTF and the neural contrast sensitivity function (determined using laser interference fringes), 2) to investigate the influence on the extent of nuclear cataract on the MTF, 3) to compare the relative significance of CS tests and MTF tests for detecting change in the eyes of Visual function following cataract surgery and 4) to determine the sensitivities of CS tests, MTF tests and visual acuity tests to the extent of cataract development as assessed during slit lamp examination.